The invention involves short-arc lamps and, in particular, xenon short-arc lamps of high power. Moreover, the invention can also be applied to other short-arc lamps such as mercury short-arc lamps and to DC lamps whose anode has a large diameter. A preferred application is in discharge lamps for still image applications (for example large image slide projection) and digital projection techniques, where the arc movement is more strongly perceived, since there is no movement of the film.
The problem of arc instability has previously been regarded essentially only as an electrode phenomenon. Efforts made to date have attempted only to find an electrode shape which is suitable for the discharge and is as favorable as possible in terms of flow (U.S. Pat. No. 5,818,169). However, no account has been taken of the turbulent reverse flow in lamp bulbs. Thus, turbulent disturbances of the discharge arc by the gas flowing in reverse cannot be avoided.
The following measures have so far been applied to minimize arc instability:
1. Reduction of the filling pressure in simultaneous conjunction with increasing the arc spacing, in order to obtain the same lamp voltage with the same current. However, for photo-optical applications it is important to have an arc spacing which is as small as possible in order to simulate a light source which is as punctiform as possible.
2. Reduction of the current, since the instances of gas turbulence also become smaller with a smaller current. However, it is disadvantageous in this case that the radiant flux is also reduced thereby.
3. Operation of the lamp in a vertical burning position with the anode on top. However, this considerably limits the field of application.
All these measures combat the consequences of the turbulence rather than preventing them from occurring.
It is an object of the present invention to provide a short-arc lamp which is distinguished by very low arc instability.
This and other objects are attained in accordance with one aspect of the present invention directed to a short-arc lamp with a discharge vessel which, in addition to a filling medium, contains an anode and a cathode which are opposite one another. The filling medium contains inert gases and/or metal vapors. At least the anode comprises a substantially cylindrical body with two end faces. Provided in the region of the front half of the cylindrical body is a projection whose radial length projects at least 0.5 mm beyond the cylindrical body.